Boomstick Desperado Scum
 Hive Scum Build - Warhammer 40k: Darktide 

The general idea here is to leverage the Both Barrels blessing on the double-barrel shotgun to get very fast reload speed for more unlimited-ammo blasting during Desperado. Killing close-range targets gives 30% reload speed from Speedloader in addition to the 70% from Both Barrels to make you reload twice as fast as normal. Man-Stopper drastically increases the shotgun's cleave to kill more targets per shot, and the build can pretty reliably maintain 60% crit chance for the shotgun. Ammo Jack rounds up, so you get 3 rounds per reload.

Melee weapon is down to personal preference. I chose the shivs for mobility, attack speed, crit scaling, and effectiveness against crushers, but I think most weapons would work fine. You definitely want something that's decent against crushers because the shotgun is ineffective against them.

I picked rending on the cartel stimm for better damage against flak; that will bring you to 30% when paired with Pick Your Targets on Desperado. The shotgun has poor crit/weakspot damage scaling, so I don't think it's worth picking the finesse or crit nodes on the stimm unless you're trying to buff your melee DPS.

Gunslinger aura isn't necessary since you have unlimited ammo during Desperado and can also restore your ammo reserves to 20% with Pickpocket. In Havoc, you probably want to bring Gunslinger for your teammates anyway. In Auric and below, I would just stick with the Anarchist aura for more Man-Stopper procs and better melee DPS.

I picked Sticky Hands for reduced spread on the shotgun to kill specialists and elites more reliably. Unload isn't worth taking on this build because the "magazine spent" buff resets on each reload and our first shot while aiming will use two-thirds of the magazine, so you'd just get a partial bonus on the third shot.

Voice of Tertium is good, but I don't feel it's necessary. Precision Violence and Tis but a Scratch are more reliable for toughness recovery since they don't require kills. Calling for a Time Out and Chem Fortified are also good; you could swap a couple points around for these if you want more toughness damage reduction. Sticky Hands and Jittery are probably the best options to swap out, or Maxed Out Chems if you don't like the reduced duration on Chem Dependency.